I'm curious to know if we have some firm understanding or not of how Dunesfolk are named to indicate family. How do you know (outside of the Ul or Sil lines) that they are related?

I have one case study involving the Dunesfolk Ul line.
The first Sultan that founded Ul'dah was Sasagan Ul Sisigan.

Nanamo's parents are Sasabal Ul Sisibal and Nanasha Ul Nasha (confirmed by Fern at the E3 2015 Lorecast with Gamerescape).

So at first I thought, perhaps Sa and Si in the line is connected father to son. Perhaps daughter's take mother's (See Na of Nanasha and Nanamo).

But then we get to the 80 Sins of Sasamo and Fern's post on the topic ( WHERE IS THIS QUEST SOME DAY. WHAT ARE THESE SINS) states a sultana.

Any thoughts? Speculation?